1. Field
The invention relates generally to apparatus and methods for sensing analytes in a fluid, such as a liquid or a gas. A preferred example involves the sensing of one or more analytes in air or a gas expired by an individual for monitoring biochemical processes such as in diabetes, epilepsy, weight loss, and others occurring within that individual.
2. Background
There are many instances in which it is desirable to sense the presence and/or quantity of an analyte in a gas. “Analyte” as the term is used herein is used broadly to mean the chemical component or constituent that is sought to be sensed using devices and methods according to various aspects of the invention. An analyte may be or comprise an element, compound or other molecule, an ion or molecular fragment, or other substance that may be contained within a fluid. In some instances, embodiments and methods, there may be more than one analyte. “Fluid” as the term is used herein is used broadly to comprise a substance that is capable of flowing and that changes its shape when acted upon by a force. It includes liquids and gases, not only in their pure forms but also when in heterogeneous states, such as with slurries, suspensions, colloidal dispersions, and the like. Newtonian fluids are best suited to application in the present invention, but some degree of non-Newtonian behavior could be acceptable, depending on the specific application, and this is not intended to be limiting. “Gas” as the term is used herein also is used broadly and according to its common meaning to include not only pure gas phases but also vapors, non-liquid fluid phases, gaseous colloidal suspensions, solid phase particulate matter or liquid phase droplets entrained or suspended in gases or vapors, and the like. “Sense” and “sensing” as the terms are used herein are used broadly to mean detecting the presence of one or more analytes, or to measure the amount or concentration of the one or more analytes.
In many of these instances, there is a need or it is desirable to make the analysis for an analyte in the field, or otherwise to make such assessment without a requirement for expensive and cumbersome support equipment such as would be available in a hospital, laboratory or test facility. It is often desirable to do so in some cases with a largely self-contained device, preferably portable, and often preferably easy to use. It also is necessary or desirable in some instances to have the capability to sense the analyte in the fluid stream in real time or near real time. In addition, and as a general matter, it is highly desirable to accomplish such sensing accurately and reliably.
An example of the need for such devices is in the area of breath analysis. In the medical community, for example, there is a need for effective breath analysis to sense such analytes as acetone, isoprene, ammonia, alkanes, alcohol, and others, preferably using a hand-held or portable device that is relatively self contained, reliable and easy to use.
Historically, breath chemistry has not been very well exploited. Instead, blood and urine analysis has been performed. Blood analysis is painful, laborious, relatively expensive and often impractical due to lack of equipment or trained personnel. Typically blood analysis has been performed in a wet chemistry or hospital laboratory. Recently, there are two products that measure β-HBA levels that are made by GDS Diagnostics and Abbott Laboratories. While these companies have made home-testing possible, blood tests are still expensive and painful and they require careful disposal and procurement of needed equipment such as needles and collection vessels. This leads to low patient compliance.
Urine analysis has been criticized as being inaccurate. Urine analysis also is not time-sensitive in that the urine is collected in the bladder over a period of time.
Thus, while blood and urine tests can provide information about the physiological state of an individual, they have been relatively unattractive or ineffective for practical application where portability or field or home use is required.
Current systems used to sense an analyte in a gas, such as gas chromatographs and spectroscopy-related devices, are expensive, cumbersome to use, they require skilled operators or technicians, and otherwise typically are not practical for field or home use. They also tend to be quite expensive. Precision in detection systems usually comes at substantial cost. Current highly-accurate detection systems require expensive components such as a crystal, specialized power source, or containment chambers that are highly pH or humidity regulated.
Some systems for measuring analytes in air operate on electrochemical principles (see, e.g., U.S. Pat. No. 5,571,395, issued Nov. 5, 1996, to Park et al.), and some operate by infrared detection (see, e.g., U.S. Pat. No. 4,391,777 issued Jul. 5, 1983, to Hutson). U.S. Pat. No. 6,658,915, issued Dec. 9, 2003, to Sunshine et al., describes using chemically sensitive resistors to detect airborne substances and requires the use of an electrical source. U.S. Pat. No. 4,935,345, issued Jun. 19, 1990 to Guilbeau et al., describes the use of a single thermopile in liquid phase chemical analysis. However, the thermopile sensor is limited to measuring a single analyte and only a single reactant is present on the thermopile. This sensor operates in the liquid phase. Each of the foregoing patents is hereby incorporated herein by reference as if fully set forth herein.